Method of decreasing the potassium content of potassium-containing zeolites

ABSTRACT

A method of decreasing the potassium content of a potassium zeolite containing calcium, such as erionite, which comprises calcining said zeolite and thereafter ion exchanging said zeolite with cations other than potassium. Potassium zeolites, such as zeolite-T, which do not contain calcium are ion exchanged with calcium cation prior to said calcining and ion exchanging. Catalytically active forms of the zeolite product are used in hydrocarbon conversion processes.

United States Patent Kokotailo et al.

[ Feb. 8, 1972 [54] METHOD OF DECREASING THE POTASSIUM CONTENT OFPOTASSIUM-CONTAINING ZEOLITES [72] Inventors: George T. Kokotailo,Woodbury; Stephen L. Lawton, Sewell, both of NJ.

[73] Assignee: Mobil Oil Corporation [22] Filed: Oct. 28, 1968 [21]App]. No.: 771,701

[52] US. Cl ..23/l1l, 252/455 Z [51] Int. Cl. ..C01b 33/28 [58]FieldofSearch ..23/l1l, 112,113;252/455Z [56] References Cited UNITEDSTATES PATENTS 2,950,952 8/1960 Breck et al ..23/1 13 3,140,251 7/1964Plank et a] ..252/455 3,402,996 9/1968 Maher et al ..23/1l2 3,375,0653/1968 McDaniel et a]. ..23/1l2 FOREIGN PATENTS OR APPLICATIONS6,607,456 1 1/1966 Netherlands ..23/1 13 OTHER PUBLICATIONS BarrerChemical Society Journal 1950 pp. 2342-2350 Eberly The AmericanMineralogist vol. 49, .Ian.-Feb.. 1964, PP. 30-40 Primary ExaminerEdwardJ. Meros Attarney0swald G. Hayes, Andrew L. Gaboriault, Raymond W.Barclay and James F. Woods ABSTRACT 3 Claims, No Drawings METHOD OFDECREASING THE POTASSIUM CONTENT OF POTASSIUM-CONTAINING ZEOLITESBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a method for decreasing the potassium content ofpotassium-containing zeolites. More particularly, this invention relatesto a method for decreasing the potassium content of zeolites containingpotassium in admixture with calcium.

2. Discussion of the Prior Art Various shape selective zeolite catalystshave been prepared from naturally occurring zeolites of the erionite oroffretite family. These zeolites can be converted into a catalyticallyactive form by ion exchange which effectuates removal of a substantialportion of the sodium content therefrom. For some unexplainable reason,the potassium content cannot be readily decreased and thus the presenceof potassium in the exchanged zeolite has a deleterious effect upon thecatalytic properties of the zeolite since most zeolite catalystspreferably have a desired minumum content of alkali metal cationstherein. The potassium content of erionite is especially difficult toreduce beneath a specific level without impairing the crystal structureof the zeolite. Thus, D. L. Peterson, F. Helferich, and G. C. Blytashave written in J. Phys. & Chem. of Solids 26, 835, (1965) that thepotassium content of erionite cannot be reduced below the level of 0.5mev./g. (1.95 percent) without destroying the crystal lattice.

It is an object of the present invention, therefore, to provide a methodfor decreasing the potassium content of erionite and related zeolites ina method which does not adversely affect the crystal lattice and inwhich the potassium content is decreased to a level beneath 1.95 weightpercent. It should be mentioned that naturally occurring samples oferionite contain some quantities of calcium.

SUMMARY OF THE INVENTION Broadly, this invention contemplates a methodof decreasing the potassium content of a potassium zeolite containingcalcium which comprises calcining said zeolite and thereafter ionexchanging said zeolite.

In a particularly desirable embodiment, this invention contemplates amethod of decreasing the potassium content of a potassium zeoliteinitially free of calcium which comprises calcining said zeolite,contacting said zeolite with a molten calcium salt or aqueous calciumsalt solution, calcining the so contacted zeolite and thereafter ionexchanging said zeolite. The present invention also contemplates a newzeolite prepared by the above method having a composition, expressed interms of mole ratios of oxides, as follows:

l.liO.4[(xM O/n):(1x)l( O]:Al O :68 SiO :8 H O wherein M is calcium, nis the valence of M, x is any value between 0.01 and 0.99 and having thecharacteristic diffraction pattern of table 1 below. Generally thezeolite has a potassium content of less than 1 .95 weight percent.

DESCRIPTION OF SPECIFIC EMBODIMENTS The method of the present inventionis particularly applicable to shape-selective zeolites of natural origincontaining calcium therein, but it is to be understood that syntheticzeolites such as zeolite-T can also be treated in accordance with thepresent method to have the potassium content reduced so that the cationsites can be filled by cations having catalytic activity. In the case oftreating zeolites containing calcium, the zeolite is calcined whichcalcination appears to remove the potassium from the small cages of thezeolite by migration of the calcium within the zeolite. Subsequent ionexchange with an aqueous solution of an exchanging salt or, preferablywith a molten calcium salt removes the potassium in exchange for thecation of the salt. Subsequent to calcination, the calcium is believedto occupy the small cages of the zeolite previously occupied bypotassium. Potassium which has moved into the large cages is removed byion exchange readily since, in those pan positions, the potassium isavailable for ion exchange in accordance with known techniques.

In treating zeolites which do not contain calcium, such as zeolite-T,the zeolite is initially calcined and then calcium exchanged,preferably, with a molten calcium salt. After the calcium exchange ortreatment, the zeolite is once again calcined to effect the theorizedcalcium-potassium migration and to displace the potassium from the smallcages of the zeolite into the larger cages. Thereafter, the zeolite ision exchanged with a cation which exchanges with the potassium now inthe larger cages of the zeolite. Preferably, this second ion exchange iswith a calcium salt, preferably a molten calcium salt as thisfacilitates reduction of the potassium content in the zeolite.

The effect of the calcination and ion exchange of a calcium zeolite isconsidered particularly unexpected and surprising. The reason for theready removal of potassium by the manipulative procedures of the presentprocedure is not fully understood especially considering the respectiveatomic radii of the potassium and calcium atoms. Specifically, thepotassium atom has an atomic radius of 2.31 angstroms whereas thecalcium atom has an atomic radius of 1.97 angstroms. Nevertheless, theexperimental data reveal that the calcium atom during calcinationapparently forces the potassium atoms, as cations, out of the smallcages of the zeolite and into the larger cages where they are readilyremoved by ion exchange.

Using the method of the present invention, the potassium content ofnaturally occurring erionite can be reduced to a level as low as 0.23weight percent after several exchanges following calcination of acalcium-containing zeolite. The reduction in the potassium content doesnot detrimentally affect the zeolite structure of the crystal lattice.Preferably, after the initial calcination of the zeolite, the zeolite isexchanged and calcined several times with a suitable salt.Representative salts used in molten form include ammonium acetate,ammonium sulfate and ammonium thiocyanate. Representative salts used inaqueous solution form include ammonium chloride, ammonium bromide,ammonium carbonate and other ammonium salts. Representative metal saltsused in molten form include silver nitrate, silver bromide, calciumbromide hydrate, calcium chloride hydrate, beryllium basic acetate,beryllium sulfide, beryllium nitrate, magnesium carbonate hydrate,magnesium nitrate hydrate, manganese chloride hydrate, manganese sulfatehydrate, zinc nitrate, zinc acetate, zinc chloride, aluminum nitrate,chromic chloride, lanthanum nitrate hydrate, samarium nitrate hydrate,copper sulfate and mercury nitrate. Representative metal salts used inaqueous solution form include salts of rare earth metals, silveracetate, silver citrate, calcium arsenate, calcium benzoate, calciumcarbonate, calcium citrate, beryllium bromide, beryllium carbonate,beryllium sulfate, barium bromide, barium carbonate, barium citrate,magnesium bromide, magnesium sulfate, magnesium acetate, manganeseacetate, zinc sulfate, aluminum acetate, aluminum citrate, titaniumchloride, zirconium chloride, zinconium sulfate, chromic acetate, ferricchloride, ferric acetate, ferrous chloride, nickel chloride, cerousbromide, lanthanum chloride, lanthanum sulfate, yttrium bromide,samarium acetate, samarium chloride, samarium sulfate. A particularlysuitable sodium salt is sodium acetate hydrate. The subsequentlyemployed ion exchange salt solutions are preferably in a concentratedform as in the form of a molten salt containing water of hydration. Theextent of the reduction in the potassium content is generally a functionof the number of exchanges to which the zeolite is subjected followingcalcination of the zeolite after it contains calcium.

It is essential in the process of the present invention that the calciumbe present either by introduction through a treatment of the zeolite orpresent by virtue of occurring in the naturally occurring zeolite.Calcium salts which can be employed to contact zeolites which do nothave any naturally occurring calcium therein include calcium nitratetetrahydrate and calcium chloride hexahydrate.

The calcination is generally performed at a temperature of at leastabout 400 C. for at least 2 hours although calcination is atime-temperature relation and it is possible under certain circumstancesto calcine at a somewhat lower temperature to cause the desiredmigration of the calcium in the zeolite into the small cages of thezeolite to force the potassium out to a position where it is availablefor subsequent ion exchange.

The resultant zeolite is a novel crystalline aluminosilicate which canbe identified by its X-ray diffraction pattern. The X-ray diffractionpattern of the zeolite is set forth in Table 1 below:

These values were determined by standard techniques employing a scanspeed of 1% per minute. The radiation was the K-alpha doublet of copper,and a Geiger counter spectrometer with a strip chart pen recorder wasused. The peak heights, 1, and the positions as a function of 2 timestheta, where theta is the Bragg angle, were read from the spectrometerchart. From these, the relative intensities, 100 1/1,, where 1,, is theintensity of the strongest line or peak and d (obs), the interplanarspacing in angstroms, corresponding to the recorded lines, wherecalculated.

Preferably, the alkali metal content, especially the sodium, isexchanged out of the composition for another cationic form as the sodiumform of the zeolite tends to be less catalytically active and stablethan other forms. The sodium and/or potassium can be largely removedfrom the aluminosilicate by ion exchange. The sodium and/or potassiumcations can be exchanged for hydrogen ions by treating thealuminosilicate with acids. Alternatively, it can be treated with asource of ammonium, alkylammonium, or arylammonium cation providingsteric hindrances do not prevent the cation from entering the cages ofthe zeolite. If the sodium and/or potassium is replaced for an ammoniumcation or complex, the hydrogen fomi is prepared therefrom by heatingthe composition at a temperature above about 400 F. causing evolution ofammonia and retention of a proton in the composition at the sitepreviously occupied by the ammonium ion.

Other replacing cations include cations of the metals of groups [A otherthan sodium and potassium, lBVIll of the periodic table; especiallymetals of groups ll and Ill, including the rare earth metals, tin, lead,group lVB comprising titanium, zirconium, and hafnium; metals of theactinide series, antimony, bismuth, chromium; also group VllIB and groupVIll. Regardless of the cations replacing the sodium or potassium in thesynthesized form of the composition, the spatial arrangement of thealuminum, silicon and oxygen atoms which form the basic crystal latticeof this material, remains essentially unchanged by the describedreplacement of sodium or potassium as determined by X-ray diffractionanalysis of the ionexchanged material. One exception is in calciumexchange which causes the C lattice parameter to shrink.

[on exchange of the zeolite can be accomplished conventionally bycontacting the zeolite with a solution, suitably an aqueous solution, ofa salt of the exchanging cation. Additionally, the composition canundergo solid-state exchange to remove sodium or potassium andsubstitute another cation therefor. Preferably, an exchange with acalcium salt is employed which may be followed by exchange with anothercat1on.

While water will ordinarily be the solvent in the base exchangesolutions employed, it is contemplated that other solvents, althoughgenerally less preferred, can be used in which case it will be realizedthat the above list of exchange compounds can be expanded. Thus, inaddition to an aqueous solution, alcohol solutions and the like of theexchange compounds can be employed in producing the exchanged catalystof the present invention. Generally, the alkali metal content is reducedto less than 5 percent by weight and preferably less than 3 weightpercent. When the exchanged aluminosilicate is prepared, it isgenerally, thereafter treated with a suitable solvent, e.g., water, towash out any of the anions which may have become temporarily entrainedor caught in the pores or cavities of the crystalline composition.

Catalytically active forms of the new zeolite can be incorporated withother materials, such as active and inactive inorganic materials, whichfunction as a matrix for the new catalyst. These inorganic materialsinclude naturally occurring clays and metal oxides. The latter can beeither naturally occurring or in the form of gelatinous precipitates orgels including mixtures of silica and metal oxides. The inactivematerials suitable serve, among other things, as diluents to control theamount of conversion in a given process so that the products can beobtained economically and orderly without employing other means forcontrolling the rate of reaction. The new zeolite can be incorporatedinto a naturally occurring clay, such as a kaolinite, which improves thecrush strength of the catalyst and makes it more suitable in commercialoperations. These inorganic oxide matrix materials function as bindersfor the zeolite. Naturally occurring clays which can be composited withthe new catalyst include the montmorillonite and kaolin family, whichfamilies include the subbentonites, and the kaolins commonly known asDixie McNamee-Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite, oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification. Binders useful for compositing with the catalyst alsoinclude inorganic oxides, notably alumina.

in addition to the foregoing materials, the catalyst can be compositedwith a porous matrix material such as silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silicaberyllia, silica-titania as wellas ternary compositions such as silica-alumina-thon'a,silica-alumina-zirconia, silica-aluminamagnesia andsilica-magnesia-zirconia. It can be formed as a cogel with one of theseporous matrix materials. The relative proportions of finely dividednovel crystalline aluminosilicate and inorganic oxide gel matrix varywidely with the crystalline aluminosilicate content ranging from about 5to about percent by weight and more usually, particularly when thecomposite is prepared in the form of beads in the range of about 5 toabout 50 percent by weight of the composite.

The novel zeolite of this invention can contain ahydrogenation-dehydrogenation component, such as an oxide of a metal, asulfide of a metal, or a metal of groups VI and VIII of the periodictable, and manganese. Representative elements which can be incorporatedin the zeolite are cobalt, nickel, platinum, palladium, ruthenium,rhodium, osmium, iridium, chromium, molybdenum, and tungsten. The mostpreferred metals are platinum, palladium, nickel, zinc and cadmium.These materials either in their elemental form, as oxides, or sulfidescan be impregnated into the zeolite or in cationic form can be exchangedinto the zeolite for a sodium or potassium cation. The methods forimpregnation and/or exchange are those commonly used in the art. Thesehydrogenationdehydrogenation components can be intimately combined byother means, as by physical admixture. The resultant catalyst,

especially in a form containing less than 4 percent by weight alkalimetal, preferably less than 3 percent, is useful in hydrocracking andreforming as well as other processes involving hydrogenation ordehydrogenation.

Employing the catalyst of this invention, lighter petroleum stock andsimilar lower molecular weight hydrocarbons can be hydrocracked attemperatures between 400 and 825 F. using molar ratios of hydrogen tohydrocarbon charge in the range between 2 and 80. The pressure employedwill vary between and 2,000 p.s.i.g. and the liquid hourly spacevelocity between 0.1 and i0.

Employing a form of the catalyst not containing ahydrogenation-dehydrogenation component, the catalyst can be employedfor catalytic cracking, using a liquid hourly space velocity betweenabout 0.5 and 50, a temperature between about 550 and 1,200 E. and apressure between subatmospheric and several hundred atmospheres.

Additionally, catalytically active forms of the zeolite of thisinvention find extensive utility in a wide variety of hydrocarbonconversion processes including hydroisomerization, hydrodealkylation,hydrodisproportionation, hydrocarbon oxidation, dehydrogenation,desulfurization, hydrogenation, hydrocracking, polymerization and thelike provided, of course, that the reactant to undergo conversion canenter the pores of the zeolite and the product can be removed fromwithin the zeolite.

In order to more fully illustrate the nature of the present inventionand the manner of practicing the same, the following examples arepresented:

EXAMPLE 1 A sample of a naturally occurring erionite zeolite having acomposition as follows:

SiOZ 7L5 weight percent Al,O3 14.9 Fe,O3 2.6 D 4.6 CaO 2.4 Na2O 4.0 MgO1.5

was calcined in air for4hours at575 C.,cooledquickly and immediatelytreated with an excess of molten Ca(N O;;) '4H;( The sample was allowedto stand overnight at 75 C. then washed in hot water and dried. Thecrystalline structure had changed as revealed by an X-ray diffractionpattern of the zeolite after then treated. The above treatment wasrepeated twice. Analysis of the so treated zeolite showed a potassiumconcentration of 0.82 weight percent and a calcium concentration of 7.0lweight percent. X-ray diffraction analysis revealed that the C latticeparameter had decreased as revealed by the shift of the 104 line from a2-theta angle of to 255. The material was a crystalline material inwhich there was no apparent destruction of the crystal. It sorbed 6.7weight percent normal hexane determined at 25 C. and under a pressure of20 mm. Hg.

EXAMPLE 2 Another sample of naturally occurring erionite having acomposition as follows:

SiOZ 70.8 M203 16.3 Fe203 L6 K20 5.2 CaO 3.3 Na20 l.3 MgO L2 was calciumexchanged as in Example I. A portion of the exchanged material was onceagain calcined, calcium exchanged and a second portion was twice againcalcined, and calcium exchanged in the manner of Example 1. Analysis ofthe thrice-calcined and -exchanged sample revealed a potassiumconcentration of 0.44 weight percent and a calcium concentration of 6.06weight percent. The normal hexane absorption of the thrice-calcined andcalcium-exchanged erionite was 7.2 weight percent determined at 25 C.and under a pressure of 20 mm. Hg.

EXAMPLE 3 EXAMPLE 4 A sample of the erionite employed in Example 2 wascalcium exchanged three times the same way as described above in Example3. Elemental analysis of the so treated zeolite showed a concentrationof 0.44 weight percent potassium and 6.08 weight percent calcium.

EXAMPLE 5 A sample of the naturally occurring erionite employed inExample 1 was calcined for 2 hours at 500 C., cooled rapidly and anexcess of molten sodium acetate, i.e., CH COONa-3 H O was added andallowed to stand for about 18 hours at 75 C. The sample was washed inhot water and dried. The above process was repeated twice. An analysisof the sample showed a concentration of 6.5 weight percent sodium and0.23 weight percent potassium.

EXAMPLE 6 A sample of the naturally occurring erionite employed inExample 2 was sodium exchanged three times as described in Example 5. Ananalysis of this sample showed a concentration of 7.5 weight percentsodium and 0.26 weight percent potassi- EXAMPLES 7 and 8 A sample ofzeolite-T prepared in accordance with U.S.P. 2,950,952 was treated inaccordance with Examples 5 and 6. Potassium content was observed to be3.1 weight percent potassium and 6.4 weight percent sodium. However whenthe sample was treated with calcium nitrate tetrahydrate and thenammonium exchanged three times, the potassium content was significantlyreduced without collapse of the crystal to 0.39 weight percentpotassium. It is thus theorized that calcium is necessary for thereduction of the potassium content and that by merely employingcalcination and exchange at high temperatures with other salts does notlower the potassium content to below 2 percent.

it should be mentioned that once the potassium content has been replacedby calcium that calcium ions can be readily exchanged in and out of thezeolite in accordance with known techniques for ion exchange. Thus, whenthe potassium is removed from the zeolite, the ion exchange resistanceof the cations in the site originally occupied by the potassium is nolonger evident.

From the foregoing, it is apparent that the method of the presentinvention is effective to substantially reduce the potassium content oferionite and similar type zeolites including especially zeolite-T andoffretite in a manner which does not cause the crystal to collapse andwhich reduces the potassium content to an amount substantially less thanthat heretofore believed possible. The resultant zeolite is useful incatalysis especially in shape-selective catalysis and is often useful asan absorbent or desiccant.

The terms and expressions used herein have been used as terms ofillustration and not of limitation, as there is no intention, in the useof such terms and expressions, of excluding any equivalents, or portionsthereof, as many modifications and departures are contemplated withinthe scope of the invention claimed.

We claim:

1. A method of decreasing the potassium content of a natural potassiumzeolite containing calcium which comprises initially calcining saidzeolite at a temperature of at least 400 C. and thereafter ionexchanging said zeolite with a molten calcium salt and repeating saidcalcining and ion exchanging until the potassium content is less than1.95 weight percent.

2. A method of decreasing the potassium content of a potassium zeolitefree of calcium which comprises ion exchanging said zeolite with amolten calcium compound, calcining the so exchanged zeolite at atemperature of at least 400 C., ion exchanging said zeolite with amolten salt of calcium capable of entering the pores of said zeolite andrepeating said calcining and ion exchanging until the potassium contentis less than l.95 weight percent.

3. A method of decreasing the potassium content of a potas sium zeolitefree of calcium which comprises ion exchanging said zeolite with amolten calcium compound, calcining the so exchanged zeolite at atemperature of at least 400 C., ion exchanging said zeolite with acation other than potassium capable of entering the pores of saidzeolite, and repeating said calcining and ion exchanging until thepotassium content is less than 1.95 weight percent.

mg? mm STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,6LO,68O m February 8, 1972 Inventor) George T. Kokotailo and Stephen L.Lawton It is certified that error appears in the above-identified patentand that aid Letters Patent are hereby corrected as shown below:

Column 3, line 3 '1 1/2 per minute" should read I --l/2 degree perminute-- Column 3, line 65 "Group VIIIB" should read --Group VIIB--Column 5, line 39 "D 0" should read "K 0" Signed and sealed this 27thday of June 1972.

(SEAL) Attesc:

EDWARD M.FLETGI-IER,JR. ROBERT GOT'I'SCHALK Attesting OfficerCommissioner of Patents

2. A method of decreasing the potassium content of a potassium zeolitefree of calcium which comprises ion exchanging said zeolite with amolten calcium compound, calcining the so exchanged zeolite at atemperature of at least 400* C., ion exchanging said zeolite with amolten salt of calcium capable of entering the pores of said zeolite andrepeating said calcining and ion exchanging until the potassium contentis less than 1.95 weight percent.
 3. A method of decreasing thepotassium content of a potassium zeolite free of calcium which comprisesion exchanging said zeolite with a molten calcium compound, calciningthe so exchanged zeolite at a temperature of at least 400* C., ionexchanging said zeolite with a cation other than potassium capable ofentering the pores of said zeolite, and repeating said calcining and ionexchanging until the potassium content is less than 1.95 weight percent.